Monday, August 9, 2010

this is a continuation of the previous part of the disassembly guide for the pentacon 135mm f2.8 (preset) lens. with most of the major sections now apart, we'll take a look at fixing the damaged aperture mechanism...

from the photo above, we can see that one of the aperture blades has dislodged and is now stuck between other blades at around the 2 o'clock position. note also the smudges on the blades, which are actually oils that most likely is what leads to the aperture damage. there is too much oils on the blades' surfaces which caused them to stick to each other and i guess is what eventually caused one of the blades to pop out from its slot due to the tensions induced when the aperture blades moves and drags against each others.

there is a 'C'-shaped plastic retaining ring [10(a)] that keeps the aperture assembly in place. one end of this retaining ring has a small slot, where one can hook a small screwdriver and pull the ring inwards to release it. from here, the slotted guide ring [12(a)] can be lifted up for removal, followed by the aperture blades [12(b-c)].

as there is so much oils on the aperture blades, the whole bunch of blades pops out in on piece [12(b)], and i had to pry them off from one another. [12(c)] shows a single blade which is the one that originally popped out of place. thankfully, there is no visible permanent damage on the blades.

[13(a)]: here, i made it easy for you to count the number of aperture blades present (15x total). the darker parts on the blades are oils, which is a lot... a commonly recommended cleaning agent for this is naphtha or lighter fluid. for me, i just wiped each blades one-by-one with a piece of tissue, and finishing by dabbing with cotton swabs moistened with alcohols.

there are additional 3 screws [14(a)] that attach the aperture mounting ring to the helicoid portion. i don't see a need to remove these though... there are 15 small holes here where one end of each aperture blades attaches to. after cleaning the aperture blades, it's time to reinstall them...

note that both ends of the aperture blades differs from each other: one end has a stud aligned at the middle [14(b)] - this stud goes into the holes in [14(a)] and pivots there. the other end has the stud offset to the edge of one side [14(c)] - this part should face upwards/to the front and goes between the slotted guide rings that we removed in [12(a)].

i forgot to take more detailed photos showing the assembly process of the blades here (oh well... i don't want to dismantle everything again just to take more photos!). anyway, the blades should be assembled as how they will be when wide-open, i.e. the entire blade should sits on the mounting ring, away from the opening hole. insert each blades by latching the stud on the correct ends into the holes in a clockwise fashion, i.e. the next blade should be inserted into the next hole in the clockwise direction (viewed from the front), overlapping the previous blade. this should be fairly straightforward for the first ten blades.

for the last 5 remaining blades, things may be a little more fiddly here as the remaining holes for attaching the blades are now covered by the previously inserted blades. here we'll need to slide these blades underneath the existing blades into position, and in the process one may accidentally dislodge the previously inserted blades from the holes. one tips here is that the other end of the blades has the studs on the edge of the blade, facing up. the inner wall right beside these studs is actually a little recessed (except at the opening slot for the aperture ring coupling mechanism), just enough to allow a tiny portion of the studs to slide under and 'lock' it in place against vertical movements. so the trick here is to push all the blades that are already inserted into this 'locked' position, and release just enough of them (should be less than 5 at the max - for the last blade) to allow you to slide the next remaining blades underneath - then push these unlocked end of the blades out just enough so that you can see the next hole to attach to underneath.

once all 15 blades have been successfully inserted, push all blades into the previous 'locked' position, and insert back the slotted guide ring [12(a)]. note that there is a hole at the side of the slotted ring where the screw from [7(a)] attaches to that couples the aperture mechanism to the aperture ring outside. the correct position of this hole, at wide-open position (when viewed from the side, with the aperture/front facing upwards, is at the far left of the slot openings (see [16(b)] further below for the slot opening/hole referenced here). make sure this is the last position at the far left before the hole disappears from view. if this hole is not visible at all, you're doing it wrong! :p

replace back the 'C'-ring from [11(a)] to secure the aperture mechanism in place. use a pin/small screwdriver to move the hole referenced above to test that the aperture is opening closing correctly. so there, we have a nice circular aperture opening again, with clean aperture blades to boot!

view of the aperture openings from the rear side [15(a)], and also the front side [15(b)] which is more commonly seen in product shots of this lens.

well, we can now proceed to reassemble the whole lens again. clean up whichever parts that may be deemed necessary, and re-grease all parts that should have grease added, if you've cleaned away the old grease (with a suitable grease of course - if you're not sure what to use, better leave the old greases alone even if they're full of dirts. it's still better than using a wrong grease that eventually seeps into the internals of the lens and coats everything, glass included). as for which parts should have grease and which part should not, well, generally i'd say if it appear to be greased previously prior to cleaning, you know what to do. but use your common sense - the aperture blades previously have greases/oils on them, but don't go and add them back after cleaning!!

the various parts should go back on in the reverse order that we've taken them off previously - just trace back the parts numberings here in reverse order. below are some additional guides at how some of the parts should align together, as a must.

to make things easy, we'll reassemble the aperture ring/control portions using the wide-open (f2.8) position as guideline. set the aperture mechanism to the wide-open position if it is not already there. the screw at [16(a)] should rest in the small slot closer to red dot at [16(e)]. meanwhile, the ring with the aperture index markings should have the small notch at [16(c)] aligned to the hole at [16(b)] such that the hole is visible through the notch with the ring fully in place. similarly, the '2.8' marking at [16(d)] should align with the red dot at [16(e)].

additionally, when reassembling the focus ring, if you did not mark the exact position for the insertion point w.r.t the helicoid during removal (which you should have done), you may find that the infinity mark do not align correctly with the red triangle [17(b)](distance indicator) at maximum focus ring turn, as well as the aperture red dot indicator [17(a)]. installed correctly, all these markings should line up together at infinity position. in this case, you can first make an estimate of the distance that the infinity mark is offset from the red triangle indicator. then slowly unscrew the focusing ring off again until the exact point it detached from the helicoid, and stop - from here turn the focusing ring just enough to compensate for the difference in the infinity mark position estimated earlier. screw the focus ring back in and check the infinity mark position again. if it is still off, repeat the previous sequence of steps again to correct the difference here. this may take a few tries before you managed to get the correct alignment.

the remaining parts should go back on without much issues. so there, all successfully assembled back together again. not that hard now right?

14 comments:

This'll come very handy in a short time, i'd like to ask you something. I'll open my pentacon because there's something wrong with the aperture ring: when i stop down there's no CLICK sound at all so there's something missing, but i don't exactly know what. Any clue...it's probably there somewhere in your pictures but i don't know where =).Also, in order to fix it i should disassemble everything like in your guide or could i stop sooner?

i assume you're not familiar with how preset lenses work? notice that there are 2 red-dots above and below the aperture values. the upper dot indicates the 'preset' value, while the lower dot indicates the current actual aperture value. there will only be 'clicks' when you're changing the 'preset' value - this is done by pulling the aperture ring forward and turning it to change the preset value. note that your 'preset' value cannot be larger than your current value - so you should ideally move the aperture ring to f2.8 first.

then in actual use, you set the aperture to max (f2.8) by turning the ring to one side for framing/composing etc., then afterwards you turn the ring fully to the other side to reach your 'preset' aperture setting for metering and taking your photo, without having to take your eyes off the camera. this is the way preset lens is designed to be used - to allow the user to quicky switch between max (wide-open) and preset (stopped-down) aperture values.

of course, you can also choose to use it the way regular (auto/non preset) lenses work in manual mode, by setting the 'preset' value to min (f32) and using the lower red-dot as your aperture indicator for setting your desired aperture values. but in this case there will be no 'clicks' when turning the aperture ring as expected because the lens is designed not to have clicks here.

so long story short, i don't think there is anything wrong with your lens - so there's no need to disassemble it.

Wonder if you can get me out of a hole. One of the grub screws broke and had to be drilled out, any ideas where to find a replacement or even better any idea how to find out the DIN or exact dimensions/spec of the offending grub screw?

thanks, that's a good idea, the problem is finding one, we have been watching ebay since the day it happened hoping to find one under £10! Seems a lot of money just for one teeny tiny grub screw! lol. Also enquired in a jewellery store but they wanted to see lens which is still in pieces in the workshop so that wasn't practical. Anyway thanks for the advice and the tutorial which was fantastic. ALWAYS remember not to remove grub screws, just loosen them!! lol

Great article thanks. One of my iris blades has come adrift and I intend to open the front and pop it back in place. First problem: I can't figure out how the metal lens hood is held in place? I have tried simply unscrewing it and it won't budge, am I missing something?

I am dealing with model 4/200mm. It is very very similar construction to 135. Hmm there are some differences. My was left dissasembled couple of years, and these days I am trying to assemble it back. In the meantime I forgot what parts are lost or broken and how all was coupled together. Finally got it assembled with some reconstruction of my own. I replaced missing bolt from 12a which should point radially out to side whole of outer ring. Outer ring which is user operated control ring for aperture setting. That is how motion of control ring transfer to the aperture. I guess.The problem is that I can't get the lowest f (22) while maximal f4 is maintained well. This completely unclear to me. I assume that some body parts (8b) which also limits this movement are rotated few mm out of original positin. But I can't unscrew them at all anymore.

Curved spring (8d) I had to make new by myself. Actually the problem with this lens started because this spring broke and then locked aperture ring to operate at all.It is all OK now, except that F 22 value.